John Dunlavy was known to match the drivers in his speakers. Today I can see why. I'm working on a project, and I was hoping to avoid buying more parts. I measured these drivers from my garage, and here's what I found:
1) I measured a pair of BG NEO8s and a pair of BG NEO3s. The NEO8s measured better than published, but one of my NEO3s was about 10dB less efficient than the other. I have no idea why. The distortion curve was also rougher than the other.
2) A few years ago, Parts Express was doing a clearance deal on a shielded version of the RS28. I bought four. I just measured half of them, and neither of them matched each other, and all of them performed worse than published.
3) I measured a single Vifa XT25 and it performed great, utterly crushing the RS28s
4) I measured a single Dayton PT2C-8. This ribbon tweeter was reputedly a cheap knock off of a Hi-Vi. I've owned it for sixteen years, have never used it. It measured fantastic, much better than my BG NEO 3s. Maybe it's not so terrible after all.
5) The best performing drivers that I measured tonight were a pair of $20 tweeters from SB Acoustics. SB19ST. I have a hunch that the well regarded 3/4" tweeters from Scan Speak are likely no better than this ridiculously low priced driver from SB Acoustics.
TLDR: don't start a project without measuring your drivers first.
1) I measured a pair of BG NEO8s and a pair of BG NEO3s. The NEO8s measured better than published, but one of my NEO3s was about 10dB less efficient than the other. I have no idea why. The distortion curve was also rougher than the other.
2) A few years ago, Parts Express was doing a clearance deal on a shielded version of the RS28. I bought four. I just measured half of them, and neither of them matched each other, and all of them performed worse than published.
3) I measured a single Vifa XT25 and it performed great, utterly crushing the RS28s
4) I measured a single Dayton PT2C-8. This ribbon tweeter was reputedly a cheap knock off of a Hi-Vi. I've owned it for sixteen years, have never used it. It measured fantastic, much better than my BG NEO 3s. Maybe it's not so terrible after all.
5) The best performing drivers that I measured tonight were a pair of $20 tweeters from SB Acoustics. SB19ST. I have a hunch that the well regarded 3/4" tweeters from Scan Speak are likely no better than this ridiculously low priced driver from SB Acoustics.
TLDR: don't start a project without measuring your drivers first.
How do you measure the drivers? And in fact, what is the best way to do it? Each on an infinite baffle (I would think this has the advantage of being able to compare and match drivers) or in the finished enclosure, each driver separately (I would think this greatly simplifies designing the xover)?
If I'm doing polar measurements I'll usually do them ground plane.
If I'm just trying to insure that my drivers pass quality control, I'll just stick them on a wire shelf and measure them.
It's a crude method, but you can hear any issues immediately. For instance, pink noise on the RS28s sounded distinctly 'grungey' and the distortion curve reflected this. I could tell the SB19s measured great before I even looked at the screen, the pink noise sounded that "clean"
From a physical examination of the RS28s, I kinda wonder if they're B-Stock or something, the voice coils just don't seem to be centered 100%. Under excursion they seem to be scraping.
If I'm just trying to insure that my drivers pass quality control, I'll just stick them on a wire shelf and measure them.
It's a crude method, but you can hear any issues immediately. For instance, pink noise on the RS28s sounded distinctly 'grungey' and the distortion curve reflected this. I could tell the SB19s measured great before I even looked at the screen, the pink noise sounded that "clean"
From a physical examination of the RS28s, I kinda wonder if they're B-Stock or something, the voice coils just don't seem to be centered 100%. Under excursion they seem to be scraping.
Seas and Scanspeak are supposed to have good quality control. And I know that my Scanspeak drivers have all been alright (Apart from the T/S parameters measuring very different to the manufacturers data sheets) but the frequency response of some Monacor tweeters I have was different enough that I had to use different crossover values on each channel.
I predict that the soon-to-be released SB Acoustics SB21SDC-C000-4 will be the new budget tweeter to beat. I also predict it'll be around $35. Let's see what the future holds! 
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